The present invention relates to a device for providing an air/fuel mixture to a combustion chamber of an engine for combustion therein, in particular for providing such a mixture in which the fuel is vaporised and substantially homogeneously mixed with air. More particularly, the present invention relates to such a device having a system of specially configured screens for mixing the fuel vapour and air, and heating elements for vaporising the fuel.
In an internal combustion engine, a fuel/air mixture necessary for the combustion process the combustion chamber of each cylinder is provided typically by a fuel injection system or a carburetor upstream of or within the inlet manifold, the combustible mixture comprising droplets of fuel of differing sizes entrained in a stream of air As is well known, at relatively lower temperatures, fuel droplets tend to be of larger diameter and less homogeneously distributed in the air strewn than at relatively higher temperatures.
The fuel entry point (typically by way of the carburetor or fuel injector) is generally distanced from the intake port of each combustion chamber by a length of ducting, typically comprising one or more bends. This length of this ducting is generally such that the stream of air therein adopts a flow velocity profile such that fuel droplets carried with the air stream are urged to a central section of the ducting, and away from its walls, which are typically at an elevated temperature due to the normal running of the engine. In fact, no matter how well mixed and vaporised the fuel/air mixture may be when it leaves the carburetor or how well the fuel injector is configured to uniformly disperse the fuel in the air stream, by the time fuel/air mixture reaches the intake manifold, and particularly the air intake duct just upstream of the air inlet port to the cylinder, its characteristics will have changed. Typically, the fuel droplets, being distanced away from the hot walls, are kept relatively cool inhibiting full fuel vaporisation, and further, the effect of the air stream enhances coagulation of droplets into larger droplets. The result is that the fuel/air mixture reaching the combustion chamber comprises a substantially fuel-rich centrally flowing portion comprising a high proportion of fuel droplets that cannot combust rapidly enough when ignited because of their relatively large size and poor availability of oxygen due to non-homogeneous mixing of the air and fuel. The higher the engine rpm, the greater the tendency for the fuel to ingrate to the center of the air stream.
Thus, a proportion of the fuel, typically between 10% and 30% or even higher, is not properly utilised by the engine for generating power, and remains unburnt, being transformed instead into pollutants that are discharged into the atmosphere, requiring expensive catalytic converters in the exhaust system for their neutralisation. Further, the incomplete combustion of the fuel also results in the formation of carbon deposits, reducing the service life of the ignition units, pistons, valves and the engine in general.
Numerous prior art devices attempt to increase fuel efficiency and reduce pollutants by increasing the vaporisation of the liquid fuel. Fuel vaporisation is achieved mechanically by passing fuel through rotating blades, past screens or swirl chambers. Alternatively, and in some cases additionally, heating devices are provided to vaporise the fuel. Examples of such devices are described in U.S. Pat. Nos. 4,108,953, 4,204,485, 5,666,929, 4,550,706 and 4,359,035. These devices variously employ a screen for mixing and in some cases also a heater for vaporising fuel, some devices being complex and expensive, while others are not suitable for retrofitting except with major modifications to the engine and/or engine bay. In any case, the devices are not very effective for a number of reasons. Firstly, the devices are generally located at the carburetor/intake manifold junction. As such, the fuel/air mixture still has some distance to cover before entering each combustion chamber, with the result that the fuel droplets still cool coagulate and are urged towards the center of the ducts. A further problem with such devices utilising heaters is that the heaters are not always able to fully vaporise the fuelxe2x80x94the heating elements are disposed generally perpendicular to the direction of flow of the fuel droplets, which are thus not urged to remain in contact with the heating element for long. Thus, the contact time between the fuel and heater tends to be very small limiting severely the extent of vaporisation possible. Mixing is enhanced in the devices by the use of mesh or perforated screens. However, as has been mentioned earlier, the effectiveness of such mixing is in inverse proportion to the distance between the screen and the combustion chamber. In U.S. Pat. No. 4,295,458 a perforated open-ended cone is provided for precipitating fuel droplets at high speed on the manifold wall. However a large proportion of the fuel/air mixture continues through the open end of the cone and remains unaffected. In some embodiments, an internal component such as a turn helps swirl this flow. In any case, the effects of the cone are short-lived due to its displacement from combustion chamber entry.
There is thus still the need for a fuel/air mixer that ensures that a homogeneous air/fuel mixture comprising the smallest possible particles of fuel reaches the combustion chamber with the goal of obtaining complete combustion.
Devices for enhancing engine performance by providing water in a fine mist state are known, for example as disclosed by U.S. Pat. Nos. 3,767,172 and 4,076,002. However, while improving engine performance, use of water injection in internal combustion engines has certain drawbacks including the formation of calcium and said deposits on the valves, pistons and spark plugs.
In a second aspect of the present invention, a medium such as acetic acid solution, particularly mixed with methanol, may be inducted into the engine in lieu of water, improving performance thereof, while aiding in the cleaning of the air inlet system, combustion chamber and exhaust system during running of the engine. The methanol improves the vaporisation characteristics of the acetic acid and also acts as an antifreeze agent. According to this aspect of the invention, an atomise is provided for ensuring a high degree of vaporisation of the medium is provided. The medium also helps to prevent preignition of the combustion mixture in the combustion chamber, and thus substantially cheaper fuel without the usual anti-knock additives may be used, further reducing the running costs of an engine incorporating the present invention.
It is therefore an aim of the present invention to provide a device which substantially overcomes the limitations of prior art fuel/air mixing devices.
In particular, it is an aim of the present invention to provide a fuel/air mixing device incorporating a liquid fuel vaporiser for enabling high levels of fuel efficiency and low levels of pollution to be achieved for an internal combustion engine by way of fill combustion of the fuel.
It is another aim of the present invention to provide such a device that is retrofitable within existing internal combustion engines, particularly with minimal or nominal modification thereof or of the surrounding area.
It is another aim of the present invention to provide such a device that is simple to install and to operate.
It is another aim of the present invention to provide such a device that is relatively simple mechanically and thus economic to produce as well as to maintain.
It is another aim of the present invention to provide such a device that incorporates an electrically heated element for vaporising the fuel.
It is another aim of the present invention to provide such a device that incorporates a unique perforated screen for directing the fuel/air mixture along duct walls upstream of the air inlet port.
According to a first aspect of the invention, there is provided a fuel-air mixing device for installation in the air intake system of an internal combustion engine, said device extending into an air intake duct of a cylinder of an internal combustion engine towards a downstream end of the said intake duct, said device comprising:xe2x80x94first screen means having an open upstream inlet end, a closed downstream end, and a screen extending between a periphery of said upstream end and a periphery of said downstream end and comprising a plurality of outlet apertures for providing fluid communication between an upstream end of the air intake system and said downstream end of said air intake duct, said apertures adapted for enhancing atomization of liquid fuel passing therethrough; and mounting means for mounting said screen means within said air intake duct.
In a second aspect of the invention, there is provided combustion stability means for use in conjunction with the fuel-air mixing device comprised in an internal combustion engine, for delivering an atomised medium to a combustion chamber comprised in said engine, said combustion stability means comprising:-a refillable reservoir for holding a volume of said medium; an atomising unit; and suitable first and second fluid lines for respectively providing fluid communication between said reservoir and said atomising unit, and between said atomising unit and said intake system of said engine.